MORPHOLOGICAL-CHANGES DURING SECONDARY CRYSTALLIZATION AND SUBSEQUENTMELTING IN POLY(ETHER ETHER KETONE) AS STUDIED BY REAL-TIME SMALL-ANGLE X-RAY-SCATTERING

In this paper, we present results of morphological studies during long time melt crystallization and subsequent melting in poly(aryl ether e ther ketone) (PEEK). Morphological changes were monitored via small an gle X-ray scattering (SAXS). SAXS data were analyzed via a combination of the correlation and interface distribution functions. Our analysis indicates the following: (I) The semicrystalline morphology is best d escribed by a three-phase, dual lamellar stack model. Stacks of a fini te number of lamellae and interlamellar amorphous layers are separated from each other by interstack regions of amorphous material (liquid p ockets). (2) Secondary crystallization occurs via the formation of sec ondary lamellar stacks within the liquid pockets. Secondary lamellae a re thinner than primary lamellae (70 degrees vs 120 Angstrom), and the amorphous layer thicknesses are about 47 Angstrom in both stacks. (3) The low endotherm observed during a heating scan is associated with t he melting of the secondary lamellae. (4) At room temperature, the sem icrystalline PEEK material is in a state of dilational stress (negativ e hydrostatic pressure) which may originate from the secondary crystal lization process in constrained liquid pockets.